The invention relates to an instrument for determining the depth of a hole and, in particular, a depth gauge for providing a digital measurement of the depth of a hole in a bone.
Many surgical procedures require surgeons to secure a device to the bone of a patient. In some procedures, the surgeon spans and secures one or more bones, or pieces of bone, using a bone plate and screws or other fasteners. In other procedures, the surgeon uses a screw or other fastener without another device, for example, to secure a transplanted tendon. In many procedures, the surgeon drills a hole in the bone prior to securing the fastener to the bone. With a hole in place, the surgeon can more easily select a fastener of the appropriate length. Selecting a fastener of appropriate length can be very important. If the fastener is too long, the fastener may protrude from the bone. Typically, the bone abuts against soft tissues that may be harmed if the fastener is too long. Although over-drilling through a metacarpal may result only in minor damage to the fat layer within the finger, if the fastener used after drilling is too long, the patient may experience more serious complications. For example, a fastener that protrudes may be tactilely felt by the patient, prevent soft tissues (such as tendons, ligaments, or muscles) from moving over the bone surface, or even pierce the skin. As a different example, complications such as paralysis may result from a fastener mounted in the pedicle portion of the human spine that protrudes to a point where the fastener contacts the spinal cord.
During drilling, the surgeon is typically capable of feeling when the drill has penetrated through the bone from a drop in resistance of the drill against the bone. Because the simple act of drilling does not provide an exact measurement of the depth of the bone, surgeons sometimes use an analog depth gauge to measure the depth of the hole.
Analog depth gauges typically comprise a central probe member having a barb at the distal end, and a reciprocating sleeve that encircles the proximal end of the central probe member. To measure the depth of a hole in a bone, the surgeon abuts the sleeve against the proximal side of the hole, and extends the probe member into the hole. After extending the probe member beyond the distal side of the hole, the surgeon retracts the probe member, attempting to find purchase against the distal side of the hole with the barb. Typically, a marker is secured to the central probe member and the reciprocating sleeve has a graduated scale (in inches or millimeters) along a portion of its length. The surgeon reads the measurement of depth by examining the position along the graduated scale indicated by the marker secured to the central probe member.
A number of problems are associated with the analog depth gauge. Components of the analog depth gauge are typically manufactured from surgical-grade stainless steel, with the graduated scale embossed along a portion of the length of the reciprocating member, producing a highly reflective surface. Under bright operating room lights, surgeons find it difficult to see the graduated scale of millimeter-wide length increments. An accurate measurement of depth using an analog depth gauge requires the surgeon to make a close examination of the graduated scale while holding the analog depth gauge steady. If the barb loses its purchase on the distal side of the hole, either the accuracy of the measurement is decreased or the time required for surgery must be extended to permit repositioning of the barb. In surgical procedures that require many depth measurements, these difficulties are multiplied.
There are other problems associated with the analog depth gauge. An accurate reading of the graduated scale requires the eyes of the surgeon to be properly aligned with the graduated scale. Viewed from an angle, the position of the marker relative to the graduated scale may be distorted. The eyes of the surgeon may not be properly aligned with the graduated scale while the surgeon is standing erect. The surgeon may have to bend over while using the analog depth gauge to make an accurate reading because if the depth gauge is tilted in order to make the reading, the sleeve will shift relative to the probe, making the measurement less accurate and possibly causing the barb to lose its purchase on the distal side of the hole, resulting in the same disadvantages mentioned above.
Accordingly, there has been a need for an improved depth gauge for surgical procedures.